1. Field of the Disclosure
The present disclosure relates to a magnetic sensing element through the use of a tunnel effect, the magnetic sensing element being mounted on a magnetic playback apparatus, e.g., a hard disk apparatus, or other magnetic sensing apparatuses. In particular, the present disclosure relates to a tunneling magnetic sensing element having a high rate of change in resistance (ΔR/R) free from increase in a magnetostriction value λ of a free magnetic layer. Additionally, the tunneling magnetic sensing element exhibits excellent magnetic detection sensitivity and stability, as well as a method for manufacturing the tunneling magnetic sensing element.
2. Description of the Related Art
In a tunneling magnetic sensing element (tunneling magnetoresistive element), the resistance is improved by the use of a tunnel effect. When the magnetization of a pinned magnetic layer and the magnetization of a free magnetic layer are antiparallel to each other, it is difficult for a tunnel current to pass through a tunnel barrier layer disposed between the pinned magnetic layer and the free magnetic layer and, thereby, the resistance value becomes a maximum. On the other hand, when the magnetization of the above-described pinned magnetic layer and the magnetization of the free magnetic layer are parallel to each other, the above-described tunnel current becomes easiest-to-pass, and the resistance value becomes a minimum.
Changes in the magnetization of the free magnetic layer under the influence of an external magnetic field in accordance with this principle lead to changes in voltage caused by changes in the electric resistance and so a leakage magnetic field from a recording medium is detected.
In a tunneling magnetic sensing element shown in unexamined Japanese Patent Application Publication No. 11-161919, an interface film is disposed at the interface between a barrier layer and a free magnetic multilayer.
A spin-valve magnetoresistive element is described in each of the following unexamined Japanese Patent Application Publication Numbers: 2005-191312; 2003-060263; 2006-128410; and 11-121832.
The magnetoresistive element shown in unexamined Japanese Patent Application Publication No. 2005-191312 is composed of a laminated film in which a free layer on the side in contact with a spacer is (Co(100-x)Fe(x))(100-y)Niy (15≦x≦100, 0<y<50) and a free layer disposed on the side farthest from the spacer is Ni(100-x)Fe(x) (15≦x≦25). In the magnetoresistive element shown in unexamined Japanese Patent Application Publication No. 2003-060263, a thin film insertion layer is disposed as a part of each of a pinned layer and a free layer.
In the magnetoresistive element shown in unexamined Japanese Patent Application Publication No. 2006-128410, two enhancing layers having different magnetostriction coefficients are disposed between a free magnetic layer and a nonmagnetic material layer.
With respect to the magnetoresistive element in unexamined Japanese Patent Application Publication No. 11-121832, it is described that when the Fe content in a CoFe thin film increases, the magnetostriction increases to a positive value and reaches a maximum when the Fe is about 50 atomic percent.
One of the tasks for the tunneling magnetic sensing element is to increase detection sensitivity by obtaining a high rate of change in resistance (ΔR/R), and to improve the characteristics of a playback head.
FIG. 6 is a sectional view of a known tunneling magnetic sensing element, cut from a plane parallel to a surface facing a recording medium. In the known tunneling magnetic sensing element, an enhancing layer 6, which is in contact with a barrier layer in a free magnetic layer 8 constituting a laminate T2 is formed from a CoFe alloy. Since the CoFe alloy has a high spin polarizability as compared with that of a NiFe alloy constituting a soft magnetic layer 7 of the free magnetic layer 8, when the enhancing layer 6 formed from the CoFe alloy having a high spin polarizability is disposed on the barrier layer side of the free magnetic layer 8 formed from a NiFe alloy, the rate of change in resistance (ΔR/R) can increase as compared with that in the case where the free magnetic layer 8 is formed from merely the soft magnetic layer 7 composed of the NiFe alloy.
However, according to the known configuration, the value of the rate of change in resistance (ΔR/R) is unsatisfactory, and a further higher rate of change in resistance (ΔR/R) is not achieved while the magnetostriction of the free magnetic layer is controlled at a low level.
FIGS. 7A and 7B are graphs showing the value of magnetostriction λ (ppm) of the free magnetic layer 8 versus the Fe content (atomic percent) of the enhancing layer in the case where the Fe content of the enhancing layer composed of a CoFe alloy changes from 0 to 100 atomic percent, specifically, 0, 30, 50, 70, and 100 atomic percent, with respect to the known tunneling magnetic sensing element shown in FIG. 6. In the basic film configuration of the experiment, the order of lamination is substrate layer 1: Ta (80)/seed layer 2: NiFeCr (50)/antiferromagnetic layer 3: IrMn (70)/pinned magnetic layer 4 first pinned magnetic layer 4a: Co70Fe30 (14)/nonmagnetic intermediate layer 4b: Ru (8.5)/second pinned magnetic layer 4c: Co90Fe10 (18)]/barrier layer 5 (10)/free magnetic layer 8 enhancing layer 6 (10)/soft magnetic layer 7 (40)]/protective layer 9: Ta (200) from the bottom. A numerical subscript is expressed in atomic percent, and a numerical value in parentheses indicates an average film thickness in Å.
FIG. 7A shows the case where the barrier layer 5 shown in FIG. 6 is titanium oxide (Ti—O), and FIG. 7B shows the case where the barrier layer 5 is aluminum oxide (Al—O). In both cases, the soft magnetic layer 7 constituting the free magnetic layer 8 is formed from NiFe. However, the compositions are different. In the case where the above-described barrier layer 5 is Ti—O, Ni is 86 atomic percent and Fe is 14 atomic percent, and in the case where the above-described barrier layer 5 is Al—O, Ni is 83.5 atomic percent and Fe is 16.5 atomic percent. In the case where the barrier layer 5 is Al—O, the second pinned magnetic layer 4c is Co60Fe20B20 on an atomic percent basis.
As is clear from FIGS. 7A and 7B, the magnetostriction λ of the free magnetic layer 8 increases as the Fe content of the enhancing layer formed from the CoFe alloy increases (Fe-rich) in the tunneling magnetic sensing element.
Previously, the amount of Fe in the above-described enhancing layer 6 has been controlled at a low concentration of about 10 to 30 atomic percent. This is because the magnetostriction λ (absolute value) of the above-described free magnetic layer 8 can be controlled at a low level, as is also clear from FIGS. 7A and 7B.
However, the above-described rate of change in resistance (ΔR/R) has not been able to be improved effectively.
On the other hand, when the Fe content of the above-described enhancing layer 6 increases, the above-described rate of change in resistance (ΔR/R) can increase. However, as shown in FIGS. 7A and 7B, the magnetostriction λ of the above-described free magnetic layer 8 also increases. If the magnetostriction λ of the above-described free magnetic layer 8 increases, noises are caused in a playback head, and the stability of the playback head deteriorates. Therefore, it is desired that the rate of change in resistance (ΔR/R) increases while the above-described magnetostriction λ (absolute value) is minimized.
As described above, in the known configuration, a high rate of change in resistance (ΔR/R) and a low magnetostriction λ (absolute value) of the above-described free magnetic layer cannot be obtained in combination. The above-described problems are not described in any patent document.
Unexamined Japanese Patent Application Publication No. 11-161919 describes the tunneling magnetic sensing element in which a thin interface film formed from Co or Co(100-x)Fe(x) (20≦x≦70) having a film thickness of 10 to 20 Å is disposed at the interface between an Al2O3 barrier layer and a sensing ferromagnetic multilayer disposed thereon. It is described that the interface film (enhancing layer) is disposed as a single layer, ferromagnetic films other than the interface film are formed from low magnetostriction materials, e.g., NiFe, and the magnetostriction of the entire sensing ferromagnetic multilayer is adjusted to 0. However, there is no description about the rate of change in resistance, and it is not clear whether a high rate of change in resistance can be obtained, even when the magnetostriction can be decreased.
Unexamined Japanese Patent Application Publication No. 2005-191312 describes that a layer (enhancing layer) having a composition of (Co(100-x)Fe(x))(100-y)Niy (15≦x≦100, 0<y<50) is disposed between the free magnetic layer (Ni(100-x)Fe(x) (15≦x≦25)) and the spacer layer, and the composition is adjusted and, thereby, the magnetostriction can be decreased. However, specific values of composition and magnetostriction are not described. Furthermore, the amount of the magnetoresistance (MR) can be increased by changing the material of the free magnetic layer. However, according to the description of Example, when laminated structures (for example, Sample 17, 20, and 23) including the enhancing layer having the above-described composition of (Co(100-x)Fe(x))(100-y)Niy (15≦x≦100, 0<y<50) on the spacer layer side of the free magnetic layer are compared, the amount of change in the magnetoresistance (MR) decreases as the Fe content of the above-described enhancing layer increases.
Likewise, unexamined Japanese Patent Application Publication No. 2003-060263 describes that when thin film insertion layers having compositions of Co50Fe50, Co90Fe10, and the like are inserted in a part of the free magnetic layer, the amount of change in the magnetoresistance increases. However, the amount of change in the magnetoresistance exhibits a maximum value at a Fe content of 50 atomic percent, and decreases as the Fe content increases. Furthermore, there is no description about the magnetostriction.
Unexamined Japanese Patent Application Publication No. 2006-128410 describes that as two enhancing layers are disposed, the Co content of the second enhancing layer is specified to be smaller than the Co content of the first enhancing layer, and the magnetostriction coefficient of the second enhancing layer is specified to be smaller than the magnetostriction coefficient of the first enhancing layer, so as to suppress an increase of the magnetostriction coefficient of the entire free magnetic layer and increase the rate of change in magnetoresistance.
However, unexamined Japanese Patent Application Publication Nos. 2005-191312, 2003-060263, and 2006-128410 relate to spin-valve magnetoresistive elements, and do not relate to the relationship between the Fe content of the enhancing layer formed from Co—Fe and the rate of change in magnetoresistance or the magnetostriction with respect to the tunneling magnetic sensing element.